OzFclass

OK, I admit I'm a novice here, my first ever turned neck chambering. Gylsie has built me a .334" neck on my .30/284 & told me to turn for .3315" -.0005", and that's about what my loaded rounds are going, if you can trust the Polish metric micrometer that came off that Greek tanker that spilled its guts on the WA coast in the mid nineties - but that's another story - and my metric/imperial conversion software. I managed to prep up the Lapua brass that Nioa replaced for me & ran the neck turn into the shoulder just enough so I have a crush fit on the unfired brass, which is dropping out of the chamber without fuss & will rechamber like they've come straight out of the sizer. All good so far.

However, fired cases don't accept a projectile, which doesn't necessarily surprise me with case necks going only .011" or so & around three thou wriggle room, but apart from suck it & see, how the heck do you decide what size bushing to run over them to prep? I'm molying & have always found a bit of jump works for that scenario with my other chamberings, so soft seating isn't on my agenda at the moment.

Suggestions, please.

PS: The Wilson micrometer seating die I bought has the usual close tolerances of that manufacturer, but I was surprised to find a degree of variation in base diameter of the new brass. Some entered the die easily & some were varying degrees of snug fit, to the degree that I had to use a suitable tool to extract the worst of them. If you have the same problem, a traditional beverage can piercer of the punch formed sheet metal persuasion has all the necessary dimensional characteristics for painless & mar free extraction.

John,

Regardless of what neck thickness, I have always opted for a bushing about 0.002" less than the loaded round neck measurement, so in your case (no pun intended) that would be about 0.329" if your loaded rounds are 0.331". I use a teaspoon in the extractor ring to get stuck cases out of the Wilson.

Alan

Thanks, Alan.

That was about what I figured. I had a .330 lurking about & bought a .329 & .328 to tinplate my butt.

I picked up on something you said elsewhere, that you've been using N165. I've been a fan of VV powders since I started to play the match rifle game & was looking at N560 for the .30. I have a feeling that the double based stuff runs a tad less peaky than their single based equivalent, but it's early days yet & I have some 2209 lying about & a bit of Reloader that was given to me to fiddle with.

John

Hi All
Just want to confirm loaded round clearance on a neck turn chamber.
I have a 284 with a .312
Thanks

Tim,
In my 284 Win, I have a 0.313 Chamber, and my loaded round is 0.310 after I turn the necks down to 0.013" (013 +284 +013 = 310)
I went for 0.003" clearance after finding a lot of posts online regarding any less being " too little clearance" with subsequent accuracy problems. There could well be plenty of consistently accurate 7mm rifles with 0.002 or less clearance, but 0.003" works for me.
I use a 0.309 titanium bushing, so in theory I am using 0.001" neck tension
Tony

john,
if you are pulling necks up to 30 cal from 6.5, you are working the brass a fair bit.
this will give it more springback than softer brass, making bullets a tighter fit in fired brass.
if you are on the borderline of neck thickness, sometimes an anneal can alter this situation, and is worth a try prior to more turning.
there is a theory that 0.004 total clearance is better for 7mm and up, but Alan's findings might suggest otherwise.
often, 0.003 will be tight.
a good ball mike is a very handy tool when neckturning, but overall loaded neck diameter measured with a micrometer must be the overriding decider.
as you fire your cases more, they could become uniform in the seater, at which time a light polish of the die will make them a perfect fit.
good luck with the project and have fun.
keep safe,
bruce.

Bruce,

Don't have a ball mike, but I have one with a 2mm cylinder anvil & I've ground the point of the spindle down to a maybe 1.5 mm nose. Neck thickness measurements correlate to overall loaded diameter.

I take your point about work hardening, but I'll nut out whether or not it's an issue when I've finished fireforming.

John